From: Nathan Smith (stryyker_at_keypoint.com.au)
Date: 2003-12-02 03:37:31
----- Original Message -----
From: "Brian Ketterling" <tweel8502@hotmail.com>
To: <cbm-hackers@cling.gu.se>
Sent: Tuesday, December 02, 2003 12:51 PM
Subject: Re: Assemblers for the 65816 processor
> Hi --
>
> By the way, I have a question about SCPU RAM that Maurice Randall
couldn't
> help me with. There's that page of "user" RAM in the $Dxxx(?) area,
which I
> thought might be handy for an alternative zero page or something.
However,
> CMD advised that if you want to write to it, which requires enabling
the
> hardware registers, you should do so and then slam the lid shut
again as
> fast as possible. If your program doesn't write to the shadow
registers,
> why is this necessary? It *seems* overly cautious.
>
> Also, if I may say... that little booklet that comes with the SCPU
is pretty
> pathetic. The SCPU could REALLY use a P.R.G., I think.
>
> -- Brian
>
From memory it is $d3xx (or was it $D2xx?) so it uses what C64
normally mirrors the VIC to. I guess you do it quickly so no
accidental writes. There may be some IO reasons too which the CPLD
addresses.
I do agree a nice reference would be nice. So many of the registers
are not documented even if they are not supposed to be used.
Anyone checked how well the IO mapping is handled for stack is moved
there? It always writes to RAM? Movable stack is something very useful
missing from 6502/6510, imagine bytes and cycles saved.
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